1. Field of the Invention
The present invention relates to halide ion-sensitive devices, and particularly to halide ion-sensitive devices such as electrodes which can be used to determine the concentration of certain halide ions in a solution in a short period of time without significant interference from other halide ions or other materials, such as uric acid, which may also be present in the solution.
2. Description Relative to the Prior Art
Ion-sensitive electrodes comprising a layer of silver in electrochemical contact with a layer of silver halide (especially silver chloride) are well known. Descriptions of silver/silver chloride electrodes may be found, for example, in U.S. Pat. Nos. 3,883,495; 3,502,560; 3,591,482; and 3,856,649, and in Research Disclosure No. 16113, Volume 161, September, 1977.
Such electrodes can be useful as reference electrodes and also as sensing electrodes for detecting chloride ions in aqueous solutions. However, in measuring chloride ion activity with a silver/silver chloride electrode in order to determine chloride ion concentration in a solution, significant errors or bias in the determination can result due to the presence in the solution of other materials, such as bromide ions or uric acid, which may come into contact with the electrode.
U.S. Pat. No. 3,591,482 describes a silver/silver chloride electrode which is overcoated with a layer of alkyl methacrylate to protect the electrode from physical damage and corrosion, while permitting passage of chloride ions.
R. P. Buck, "Virtues and Limitations of ISE for Measurements in Biological Systems", plenary lecture, Proc. Analyt. Div. Chem. Soc., November, 1977, pages 332 through 334, discusses ion-selective electrodes containing various surface coatings. The particular overcoats described herein are not disclosed.
U.S. Pat. No. 3,979,274 recognizes that an enzyme electrode, such as a platinum electrode, which measures hydrogen peroxide activity, can encounter interference from substances such as uric acid or other low molecular weight materials. It describes a laminated overcoat comprising two layers bonded together by an enzyme preparation to permit passage of hydrogen peroxide but prevent passage of other materials. One of the layers may comprise a cellulose ester, silicone rubber, or methyl methacrylate. No suggestion is made that such overcoats would serve any useful purpose on halide ion-sensitive electrodes.
U.S. Pat. No. 3,694,163 describes an enzyme electrode overcoated with a phase-inverted cellulose ester material containing a reagent and an amide swelling agent. It is not suggested that such a layer could be used with a halide ion-sensitive electrode, or would have any effect on possible interferents.
U.S. Pat. No. 3,912,614 describes a noble metal electrode coated with a membrane comprising polyhydroxyl ethyl methacrylate to allow passage of oxygen, but prevent diffusion of other materials. The membrane must be 100 to 500 microns thick, according to this patent. Such a membrane, to accomplish its purpose, will necessarily result in long response times in making each measurement; i.e., the thicker the membrane, the longer the time required to make an accurate measurement after the sensing device is brought into contact with the solution under investigation.
Long response times are particularly undesirable in situations where numerous analyses must be made each day, or where numerous analyses are intended to be made by an automated or semi-automated assembly-line type analytical method.
Accordingly, it would be desirable to provide a sensing device for the detection of halide ions in solution which utilizes an overlayer to prevent interference by other materials, but wherein the overlayer is relatively thin (e.g., 1 to 8 microns), so that an accurate analysis could be carried out within a relatively short period of time (e.g., within 5 minutes) after the device is brought into contact with the solution to be analyzed.